LP3950 Datasheet, PDF (31/38 Pages) National Semiconductor (TI) – Color LED Driver with Audio Synchronizer

LP3950
www.ti.com
SNVS331C – NOVEMBER 2004 – REVISED APRIL 2013
V_DD = 2.7V TO 2.9V
V_DDIO
C_{VDD_IO}
100 nF
R_SO
100 k:
MICROCONTROLLER
V_DD = 2.7V TO 2.9V
R4
100 k:
R₃
100 k:
+ ^{LMV321 C110nF}
-
C₄ R₁
R₂
100 k:
100 nF 10 k:
SINGE ENDED
NC
AUDIO SIGNAL
NC
R_T 82k
C_VREF
100 nF
C_VDD1
100 nF
C_VDD2
100 nF
V_DD1
V_{DD_IO}
V_DD2
V_DDA
C_VDDA
100 nF _{VIN = 3.0V TO 4.5V}
C_IN
L₁
10 PF 4.7 PH
SW
IF_SEL
FB
SO
PWM_LED
SCK
R1
SI
SS
NRST
LP3950 ^G1
ASE
B1
AD1
AD2
RT
R2
V_REF
DME
G2
AMODE
GND_RGB
GND_BOOST
B2
GNDA GND1 GND2 GND3
R_R1
R_R2
R_R3
R_R4
BACKLIGHT LEDS
R_G1
R_G2
R_G3
R_B1
R_B2
R_B3
KEYPAD LEDS
AUDIO SYNC. FUNLIGHT
R_R5
R_R6
R_G4
R_G5
R_B4
R_B5
D₁
C_OUT
10 PF
Figure 34. Backlight and Keypad LEDs Controlled by the Pattern Generator
Funlight LEDs Controlled by Audio Synchronization
There may be cases where the audio input signal going into the LP3950 is too weak for audio synchronization.
This figure presents a single-supply inverting amplifier connected to the ASE input for audio signal amplification.
The amplification is +20 dB, which is well enough for 20 mV_p-p audio signal. Because the amplifier (LMV321) is
operating in single supply voltage, a voltage divider using R₃ and R₄ is implemented to bias the amplifier so the
input signal is within the input common-mode voltage range of the amplifier. The capacitor C₄ is placed between
the inverting input and resistor R₁ to block the DC signal going into the audio signal source. The values of R₁ and
C₄ affect the cutoff frequency, f_c = 1/(2*Pi*R₁*C₄), in this case it is around 160 Hz. As a result, the LMV321
output signal is centered around mid-supply, that is V_DD/2. The output can swing to both rails, maximizing the
signal-to-noise ratio in a low voltage system
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